The position, advertised last week on jobs.ac.uk, required applicants to commit to working at least two days a week on a “voluntary basis” on a new clinical study of mental illness in Birmingham’s School of Psychology.

The successful applicant was required to be an “excellent graduate” who was “keen to learn core research skills for clinical assessment” and had access to a car. They would be reimbursed for fuel and provided with office space and “regular supervision” by the study’s directors.

Sally Hunt, general secretary of the University and College Union, said that not paying researchers “undermines the principles of equal pay and is discriminatory”.

“Unpaid internships have caused concern about access to the professions, especially where there is an oversupply of graduates and an under-supply of paid employment opportunities,” she said.

“Clearly not everyone can afford to work for nothing and universities need to recognise the importance of people being paid properly for their work.”

Rebecca Boden, professor of critical management in the University of Roehampton’s business school and a former tax inspector, agreed that unpaid research positions were “fundamentally quite exploitative”.

She said a better way for universities to recruit cost-free assistance would be to recruit PhD students and to waive their fees.

Professor Boden said that in her opinion Birmingham’s advert was illegal. “You can’t get around the minimum wage legislation by calling something a voluntary position. Everything about this position says ‘job’,” she said.

In a statement, Birmingham says that its School of Psychology receives many requests from graduates seeking “the additional experience essential to secure places on programmes such as the highly competitive clinical psychology doctorate”.

“Rather than responding to individual enquiries, which is common practice, the university wanted to make this opportunity available to all and not just favour those with existing networks and contacts,” the statement says.

“Although the honorary research assistantships were conceived as training positions, the university recognises that this was not clear and has, consequently, withdrawn the advertisement.

“The university is strongly committed to providing appropriate training and support to students and graduates and has a sector-leading internship programme.”

Kevin Poulter, an associate at law firm Bircham Dyson Bell, said he had not previously come across an unpaid position in the academy.

He warned that even if Birmingham found someone willing to carry out the role for no pay, any breakdown in relations with that person could result in the university facing an employment tribunal claim for retrospective payment of the minimum wage.